FIG. 12 shows a schematic transverse cross-sectional view of a rotary electric motor 200.
As shown in FIG. 12, the rotary electric motor 200 comprises a substantially cylindrical stator 201, a rotor (not shown in FIG. 12) disposed in the central opening of the stator 201, a plurality of stator coils 202 wound around a plurality of teeth of the stator 201, and a bus ring unit 210 for electrically connecting the ends of the stator coils 202.
The bus ring unit 210 has single-phase bus rings 211, 212, and 213 for electrically connecting in-phase stator coils 202, and a neutral-point bus ring 215 for electrically connecting electrically neutral points of the stator coils 202.
In FIG. 12, the single-phase bus rings include three bus rings, i.e., the U-phase bus ring 211, the V-phase bus ring 212, and the W-phase bus ring 213.
With respect to the bus ring unit 200, it is desired that the overall size both in the axial direction and in the radial direction of the stator is reduced and, moreover, it is desired to facilitate the connecting work for connecting the ends of the stator coils 202 to the single-phase bus rings 211, 212, and 213 and the neutral-point bus ring 215, while preventing the single-phase bus rings 211, 212, and 213 and the neutral-point bus ring 215 from interfering with each other.
For example, Patent Document 1 below discloses a bus ring unit comprising a holder that is made of insulating resin and disposed on one side in the axial direction of a stator, and first to third single-phase bus rings and a neutral-point bus ring that are attached to the holder.
The holder has first to third single-phase circular grooves that are open toward one side in the axial direction (the side facing away from the stator) and to which the first to third single-phase bus rings are respectively attached, and a neutral-point circular groove that is open toward the other side in the axial direction (the side facing the stator) and to which the neutral-point bus ring is attached.
The first single-phase bus ring has a first circular part with a first diameter and first connecting terminals extending radially outward from the first circular part.
The second single-phase bus ring has a second circular part with a second diameter that is smaller than the first diameter and second connecting terminals extending radially outward from the second circular part.
The third single-phase bus ring has a third circular part with a third diameter that is smaller than the second diameter and third connecting terminals extending radially outward from the third circular part.
The first single-phase circular groove has the first diameter to receive the first circular part.
The second single-phase circular groove has the second diameter to receive the second circular part, and the depth of the groove is smaller than the first single-phase circular groove.
The third single-phase circular groove has the third diameter to receive the third circular part, and the depth of the groove is smaller than the second single-phase circular groove.
In the first single-phase bus ring, the first connecting terminals are formed such that the distal ends are positioned in predetermined positions that are more radially outward than the holder when the first circular part is attached to the first circular groove.
In the second single-phase bus ring, the second connecting terminals are formed such that the second connecting terminals are displaced in the circumferential direction relative to the first connecting terminals and that the distal ends are positioned in substantially the same positions in the radial direction as the distal ends of the first connecting terminals when the second circular part is attached to the second circular groove.
In the third single-phase bus ring, the third connecting terminals are formed such that the third connecting terminals are displaced in the circumferential direction relative to the first and second connecting terminals and that the distal ends are positioned in substantially the same positions in the radial direction as the distal ends of the first and second connecting terminals when the third circular part is attached to the third circular groove.
Thus, concerning the above conventional bus ring unit, by providing the first to third single-phase bus rings so as to be mutually displaced in the axial direction, the connecting work for connecting the connecting terminals and the ends of the stator coils is facilitated, and by positioning the connecting terminals in the same positions in the radial direction, the overall size in the radial direction is reduced, while preventing the bus rings from interfering with each other.
However, in the above conventional bus ring unit, the first to third single-phase bus rings are provided so as to be mutually displaced in the axial direction as described above and, therefore, there is a problem in that the size in the axial direction is large.
Moreover, in the above conventional bus ring unit, the single-phase bus rings and the neutral-point bus ring are made from a round wire having a circular cross-section, and a dedicated holder as described above is needed to stably retain these rings. Such a dedicated holder also results in an increased overall size of the bus ring unit as well as increased costs.